This invention relates to a process for producing glucomannan gel particles which are useful as a deposit-cleaning agent to be formulated into hygenic and cosmetic preparations.
As is well-known, dental pastes generally contain a particulate material such as calcium carbonate, calcium phosphate, calcium sulfate, aluminum hydroxide or silica for removing deposit from the tooth by a scrubbing or exfoliating effect. In order to minimize damages to the enamel and gingiva, synthetic polymer beads have also been used. A particulate material is also used in cosmetic preparations. JP-A-06033416 discloses a skin-cleansing preparation containing a cross-linked polymer bead having a certain degree of elasticity.
The known scrubbing or exfoliating agents are comprised of a particulate material having a uniform physical property throughout the entire sections. It would be desirable to have a particulate material having a dual structure comprising a relatively hard core surrounded by a relatively soft shell layer in order to minimize damages to the tissue to be cleaned while retaining a sufficient scrubbing or exfoliating effect.
The above need may be met by the present invention. According to this invention, there is provided a process for producing a particulate glucomannan gel comprising:
adding a glucomannan-rich flour in an aqueous ethanol containing about 40 to 50% of ethanol;
allowing the flour particles to swell in the aqueous ethanol;
treating the swollen flour particles with an alkali to form gelled flour particles;
separating the gelled flour particles from the liquid; and
drying the gelled flour particles.
The particulate glucomannan gel produced by the above process is particularly suitable for use in hygenic and cosmetic preparations as a deposit-scrubbing or exfoliating agent. The dried gel particles can absorb only a limited amount of water to form a dual structure in which a shell of water-swollen gel surrounds a core of the dried gel. This property is particularly advantageous over the known particulate materials because damages to the tissue to be cleaned are minimized while retaining the scrubbing or exfoliating effect of the particulate material.
Another advantage over the known particulate materials is their massage effect on the skin. The dry gel particles swell to a spherical shape having an adequate size and hardness for rolling on the skin to give the massage effect when absorbing water. At the same time, the rolling gel particles remove, fatty secretional products from the skin. This gives a pleasant feeling to the user.
Glucomannan is a polysaccharide complex found in the tuber of Amorphophallus species such as A. Konjac. Aqueous solutions of glucomannan in the form of a hydrosol produce a water-insoluble, thermally irreversible hydrogel when reacting the sol with an alkali. This process has long been utilized in Japan, China and other countries for the production of a foodstuff called xe2x80x9ckonjacxe2x80x9d from Amorphophallus tuber flour called xe2x80x9ckonjac flourxe2x80x9d.
Any glucomannan-rich flour derived from tubers of an Amorphophallus species, typically A. konjac may be employed. Purified glucomannan flour and refined konjac flour are preferred. Crude glucomannan-containing flour commonly referred to as xe2x80x9cKonjac flourxe2x80x9d is a product obtained by slicing, drying and grinding whole tubers of an Amorphophallus species, typically A. konjac to a particle size of 0.5 mm or less. Refined konjac flour is produced by pneumatically classifying the crude konjac flour to remove starch or other impurities and has a carbohydrate content of about 80% or higher by weight. Purified glucomannans are produced from crude or refined konjac flour either by washing with water or by precipitating with ethanol to increase the glucomannan content to greater than 90% or higher.
Rapidly dissolvable Konjac flour is produced by grinding the refined konjac flour into finer particles either in the presence of ethanol or in a frozen state. All of these products are commercially available.
The term xe2x80x9cglucomannan-rich flourxe2x80x9d as-used herein collectively refers to refined konjac flour, purified glucomannan flour and rapidly dissolvable konjac flour.
According to the present invention, the starting glucomannan-rich flour is added to a mixture of water/ethanol containing 40 to 50% of ethanol. Since glucomannan is not soluble in ethanol, the flour particles swell with water in the mixture without dissolving in the mixture.
According to the present invention, the glucomannan-rich flour is allowed to react with an alkali added to the water-ethanol mixture in the swollen state thereby to give discrete particles of irreversible glucomannan hydrogel. The alkali addition may be performed by initially dissolving an amount of alkali in the water-ethanol mixture or adding a solution of alkali following the addition of glucomannan-rich flour to the water-ethanol mixture.
Any alkali such as sodium hydroxide, sodium carbonate, potassium hydroxide or potassium carbonate may be used. A saturated lime water may be preferably used as is common practice in the production of edible konjac. The resulting hydrogel particles are separated from the liquid medium by the conventional method such as centrifugation and then washed well to remove excessive alkali. If necessary, the excessive alkali may be neutralized with a nontoxic organic acid such as acetic or citric acid.
The hydrogel particles are then dried in a drying apparatus preferably at a temperature of about 105xc2x0 C. Once the hydrogel particles have been dried, they do not fully revert to the original hydrogel particles in water but the dried hard gel particles can absorb an amount of water to form semi-swollen gel particles having a particle size comparable to the particle size of the starting glucomannan-rich flour. The semi-swollen particle comprises a relatively soft shell portion and a relatively hard core portion. It is for this reason that the glucomannan particles of the present invention have no or little damaging effect on the tooth or skin while retaining a sufficient deposit-removing effect when formulating in hygenic or cosmetic preparations including toothpaste and skin-cleansing preparations.